Christophe Maunoury

Myocardial perfusion in children with sickle cell disease

A lthough brain, bone, and spleen strokes are well documented in children with sickle cell disease (SCD), the myocardium seems to be spared by thrombotic events.1 However, cardiac events and myocardial ischemia have been reported in children with SCD.2–5 Detection of myocardial ischemia before cardiac complications may improve the management of patients with SCD. Noninvasive techniques such as exercise testing and echocardiography have failed to diagnose myocardial ischemia.6 Myocardial singlephoton emission computed tomography (SPECT) can be an alternative approach for the detection of myocardial ischemia.7 This prospective report assesses myocardial perfusion with thallium-201 (Tl-201) SPECT in children with SCD. • • • Myocardial perfusion was studied in 23 consecutive patients with SCD and was assessed by Tl-201 SPECT after stress and 3 hours later after reinjection, on a single-head camera equipped with a lowenergy, all-purpose collimator. A dose of Tl-201 was injected at peak exercise or during the pharmacologic or mixed stress testing (dose [megabecquerel {MBq}] weight (kilograms) 1.5) . Another dose of Tl-201 was injected before the redistribution acquisition (dose [MBq] weight (kilograms) 0.5). No patient required any sedation. The matrix size format was 64 64. Starting from the left posterior oblique position to the right anterior oblique position, 30 projections over 180° were collected at 30 seconds/step. Left ventricular ejection fraction was assessed by equilibrium radionuclide angiography, which is a simple and reliable method to quantify left ventricular ejection fraction in children.8,9 Following a standard protocol, left ventricular ejection fraction was assessed at rest on the same day with the same camera. The matrix size format was 64 64. Left anterior oblique and lateral views were performed at 5 million counts/view. Study group consisted of 10 females and 13 males, age range 3 to 19 years (median 11; Table 1). Four patients had cardiac symptoms (2 angina, 2 heart failure), 10 had atypical chest pain, and 9 were not symptomatic (Table 1). Myocardial perfusion was normal in 9 of 23 patients (Table 1). In the 14 patients with abnormal perfusion, 9 had reversible defects and 5 had fixed defects (Figure 1). The 4 patients with cardiac symptoms had an impairment of myocardial perfusion. Selective coronary angiography was performed in these 4 patients and was considered normal in all of them. The left ventricular cavity was enlarged in 14 of 23 patients. There was no chest pain during stress. The electrocardiogram during stress was abnormal in 8 of 23 patients (ST depression 1 mm); 2 patients had a normal perfusion, 4 had reversible defects, and 2 had fixed defects. In one patient (patient no. 2) with reversible perfusion defects in the inferior and anterolateral walls, myocardial SPECT was repeated six months later after treatment with hydroxyurea. Myocardial perfusion was globally improved. The left ventricular ejection fraction (mean 1 SD) was 63 9%. There was no relation between myocardial perfusion, left ventricular dilation or function, and the level of anemia. • • • In a previous study of a small pediatric population with SCD, we reported a high incidence of myocardial ischemia that was not related to left ventricular dysfunction.7 In this prospective study of 23 patients with SCD, we found an impairment of myocardial perfusion in 61% (14 of 23) of cases, with myocardial ischemia present in 39% (9 of 23) of cases. Myocardial ischemia is an underestimated complication in patients with SCD, partly because of the low sensitivity and specificity of usual noninvasive investigations.6 Moreover, myocardial infarction was observed in autopsied patients with SCD without atherosclerosis.4 SCD was treated as an independent risk factor for sudden death in young adult patients.10 Exercise testing had a low positive predictive value of myocardial ischemia. The significance of ST depression in SCD has been raised by other studies.6,11 Stress echocardiography may increase sensitivity for the detection of myocardial ischemia in patients with SCD, but this technique is cumbersome and not suited to a pediatric population. Coronary angiography can only detect lesions in the epicardial vessels. The 4 symptomatic patients with abnormal perfusion underwent a coronary angiography that was considered normal in all of the patients. These findings confirmed the autopsy studies in patients with SCD.4,12 None of them found any lesions in the epicardial vessels. Abnormality of the microcirculation was the hypothesis used to explain myocardial ischemia in patients with SCD. Myocardial perfusion abnormalities have not been validated by a reference standard method. In addition, From the Service de Medecine Nucleaire, Cardiologie Pediatrique, et Pediatrie Generale, Hopital Necker-Enfants Malades, AP-HP, Paris, France. Dr. Maunoury’s address is: Service de Medecine Nucleaire, Hopital Necker-Enfants Malades, 149 rue de Sevres, 75743 Paris Cedex 15, France. E-mail: christophe.maunoury@nck.ap-hop-paris.fr. Manuscript received August 8, 2002; revised manuscript received and accepted September 25, 2002.

Phantom evaluation of simultaneous thallium-201/technetium-99m aquisition in single-photon emission tomography.

This study investigated downscatter effects in cardiac single-photon emission tomographic studies with simultaneous thallium-201/technetium-99m acquisition, and evaluated a previously proposed subtraction technique for downscatter compensation. Ten studies were carried out with different defect sizes and locations and varying activity distributions using four energy windows: 70±10% keV, 140±10% keV, 100±10% KeV, and 103±16% keV. The subtraction technique used the 100 or 103-keV data to remove scattered99mTc counts from the 70-keV data. The size and contrast of infarcts in the dual-isotope 70-keV image were artificially decreased compared to those in the 140-keV image, caused by scattered99mTc counts that were comparable to the primary201T1 counts in the 70-keV window. The subtraction technique produced larger defects and more heterogeneous activity in the myocardial wall in dual-isotope 70-keV images compared to the corresponding201T1on-ly images. These artifacts were caused by the markedly different spatial distributions of scattered99mTc counts in the 100-keV (or 103-keV) window as compared with the 70-keV window. It is concluded that scattered99mTc photons may cause overestimation of ischemia and myocardial viability in simultaneous dual-isotope patient studies. The proposed subtraction technique was inaccurate and produced image artifacts. Adequate downscatter compensation methods must be developed before applying simultaneous201Tl/99mTc acquisition in clinical practice.